Adenosine Diphosphate Glucose Pyrophosphorylase Research Articles

Grain Chalkiness Is Decreased by Balancing the Synthesis of Protein and Starch in Hybrid Indica Rice Grains under Nitrogen Fertilization.

The important reason for the commercial value of hybrid rice suffering is due to excessive chalkiness, and the biosynthesis of starch and proteins is critical for regulating chalkiness; however, it is currently unclear how the application of N fertilizer affects grains to reduce their chalkiness and improve their quality. The 2019, 2020, and 2021 trials were conducted in a split-plot design, with high and low chalky varieties as the main plot and N fertilizer rate as the split-plot. The effects of fertilization with 75, 150, and 225 kg N ha-1 on the dynamic synthesis of starch, protein, and endogenous hormones and on the amino acid of hybrid indica rice kernels with different degrees of chalkiness were investigated. Grain physiological activity was higher in low-chalky varieties than in high-chalky varieties, and these physiological parameters were strongly associated with chalkiness formation. Higher N fertilization (150 and 225 kg N ha-1) significantly reduced the proportion of chalky grains (8.93-28.02%) and chalkiness (8.61-33.99%) compared with 75 kg N ha-1. Increased N fertilization decreased the activities of granule-bound starch synthase and starch-debranching enzyme, but significantly increased adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase, and starch-branching enzyme activities, synergistically improving glutamate synthetase and glutamine synthetase enzyme activities, which tended to support the synthesis of amylopectin, α-ketoglutarate, and 3-phosphoglyceric acid-derived amino acids in the endosperm cells of the grains; this favored starch and protein accumulation in the grains at 6-30 days after anthesis. Additionally, N application promoted the synthesis of endogenous hormones 1-aminocyclopropane-1-carboxylic acid, gibberellins, and abscisic acid in grains. Hence, N fertilization reduced the rice chalkiness in hybrid indica rice varieties by balancing grain protein and starch composition and enhancing some endogenous hormone synthesis.

Serine 31 Phosphorylation-Driven Regulation of AGPase Activity: Potential Implications for Enhanced Starch Yields in Crops.

ADP-Glc pyrophosphorylase (AGPase), which catalyzes the transformation of ATP and glucose-1-phosphate (Glc-1-P) into adenosine diphosphate glucose (ADP-Glc), acts as a rate-limiting enzyme in crop starch biosynthesis. Prior research has hinted at the regulation of AGPase by phosphorylation in maize. However, the identification and functional implications of these sites remain to be elucidated. In this study, we identified the phosphorylation site (serine at the 31st position of the linear amino acid sequence) of the AGPase large subunit (Sh2) using iTRAQTM. Subsequently, to ascertain the impact of Sh2 phosphorylation on AGPase, we carried out site-directed mutations creating Sh2-S31A (serine residue replaced with alanine) to mimic dephosphorylation and Sh2-S31D (serine residue replaced with aspartic acid) or Sh2-S31E (serine residue replaced with glutamic acid) to mimic phosphorylation. Preliminary investigations were performed to determine Sh2 subcellular localization, its interaction with Bt2, and the resultant AGPase enzymatic activity. Our findings indicate that phosphorylation exerts no impact on the stability or localization of Sh2. Furthermore, none of these mutations at the S31 site of Sh2 seem to affect its interaction with Bt2 (smaller subunit). Intriguingly, all S31 mutations in Sh2 appear to enhance AGPase activity when co-transfected with Bt2, with Sh2-S31E demonstrating a substantial five-fold increase in AGPase activity compared to Sh2. These novel insights lay a foundational groundwork for targeted improvements in AGPase activity, thus potentially accelerating the production of ADP-Glc (the primary substrate for starch synthesis), promising implications for improved starch biosynthesis, and holding the potential to significantly impact agricultural practices.

The Effect of Drip Irrigation Quota on Biochemical Activities and Yield-Related Traits in Different Drought-Tolerant Maize Varieties

Drip irrigation has a close relationship with the growth and development of maize grains and yield formation in semiarid areas. To explore the response mechanism of grain yield formation to drip irrigation quotas, a 2-year pond planting experiment was conducted under controlled conditions, by using two maize varieties with differences in drought resistance as experimental materials. Six treatments were set up, including CK1 (drought-resistant variety, 500 mm), T1 (drought-resistant variety, 350 mm), T2 (drought-resistant variety, 200 mm), CK2 (drought-sensitive variety, 500 mm), T3 (drought-sensitive variety, 350 mm), and T4 (drought-sensitive variety, 200 mm). The changes in maize grain filling characteristics, related hormones, enzyme activity related to starch synthesis, sugars and amino acids contents, and yield were analysed. The results showed that 100-grain weight at different filling times, filling rate, average filling rate, auxin, cytokinin, acid sucrose invertase, sucrose synthase, starch synthase, and adenosine diphosphate glucose pyro phosphorylase activities in maize grains decreased and the abscisic acid content and content of various amino acids and sugars in grains increased with the decrease in drip irrigation quota. The percentage of changes in drought-sensitive maize varieties was relatively high. The maize yield decreased with the decrease in drip irrigation quota. In summary, there was no significant difference in grain filling characteristics, hormone content, starch synthesis enzyme activity, and yield between maize treated with T1 (drought-resistant variety, 350 mm) and the control treatment. This effectively maintained grain growth and yield formation, achieving the goal of water saving and stable yields.

Grain chalkiness is reduced by coordinating the biosynthesis of protein and starch in fragrant rice (Oryza sativa L.) grain under nitrogen fertilization

The synthesis of protein and starch in grain is crucial for regulating rice (Oryza sativa L.) chalkiness. However, little is known about how to coordinate them in the grain to improve the appearance quality of fragrant rice under nitrogen (N) fertilizer application. In the present study, both pot and field experiments were conducted to study the effects of N fertilization on chalkiness, starch and protein content, and enzyme activities related to carbon (C) and N metabolism in fragrant rice grains. The field experiment was carried out with five N levels of 0 (N0), 64 (N64), 128 (N128), 160 (N160), and 192 (N192) kg N ha−1, and a pot experiment was additionally performed with equivalent treatments. Compared to N0, N application significantly reduced fragrant rice chalkiness grain rate (17.54–39.47 %), chalkiness area (23.79–38.54 %), and chalkiness (35.98–61.27 %) in pot and field experiments. N fertilization decreased the mean grain filling rate (0.17 mg grain−1 d−1) and extended the effective grain filling duration (3.69 d). N fertilization significantly increased the protein content (16.17–22.63 %), which was driven by the improved activities of glutamine synthetase (GS), glutamate synthase (GOGAT), glutamic oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT). Amylose and amylopectin contents, components of starch, decreased with N fertilizer application, which was associated with depression of the activities of adenosine diphosphate glucose pyrophosphorylase (AGP), granules bound starch synthase (GBSS), soluble starch synthase (SSS), and starch branching enzyme (SBE). The structural equation model (SEM) showed that N fertilization coordinated the synthesis of protein and starch and reduced the fragrant rice chalkiness by changing the process of C and N metabolism in fragrant rice grains. In short, the N fertilization decreased fragrant rice chalkiness by optimizing grain filling, balancing the protein and starch content in the grain.

Effect of Phosphorylation Sites Mutations on the Subcellular Localization and Activity of AGPase Bt2 Subunit: Implications for Improved Starch Biosynthesis in Maize

ADP-Glc pyrophosphorylase (AGPase) is a pivotal enzyme catalyzing the conversion of ATP and glucose-1-phosphate (Glc-1-P) to adenosine diphosphate glucose (ADP-Glc), thereby serving as a rate-limiting factor in starch biosynthesis in crops. Although previous investigations have suggested phosphorylation-based regulation of AGPase in maize, the explicit modulation mechanisms have yet to be elucidated. This research evaluated the effect of point mutations at phosphorylation sites (identified using iTRAQTM AB SCIEX, Framingham, MA, USA) on the subcellular localization and activity of the AGPase small subunit Bt2, and its interaction with the large subunit Sh2, in maize. Despite the induction of point mutations, subcellular localization of the Bt2 subunit remained unaltered, primarily within the cytoplasm and nucleus. The interaction between Bt2 and Sh2 subunits continued, mainly in the chloroplast. Notably, an increase in AGPase activity was observed in the case of simulated phosphorylation point mutations, whereas dephosphorylation activity significantly diminished relative to the wild type. These findings demonstrate that point mutations do not affect the subcellular localization of the Bt2 subunit or its interaction with the Sh2 subunit, but substantially modulate AGPase activity. This study provides critical insights into the role of point mutations in enhancing AGPase activity, thus potentially accelerating the production of ADP-Glc, the primary substrate for starch synthesis, promising implications for improved starch biosynthesis in maize.

Panicle removal delays plant senescence and enhances vegetative growth improving biomass production in switchgrass

Switchgrass (Panicum virgatum L.) shows great bioenergy potential and provides multiple ecological services. However, its severe seed shedding causes biomass waste and seed diffusion risk. Questions arise as to the production performance of switchgrass after panicle removal (PR), which remains unknown. We revealed switchgrass growth responses to PR and illustrated physiological reasons. Compared to the untreated switchgrass, PR significantly stimulated stem elongation (32.13%) and increased tiller number (39.70%), as well as aboveground biomass (24.69%). Importantly, PR significantly increased contents of nonstructural carbohydrates (NSCs) in the stem, which was directly beneficial to the ethanol conversion, and in the rhizome and root. The chlorophyll contents, net photosynthetic efficiency, and photochemical quantum efficiencies of flag leaf increased significantly. PR switchgrass allocated more assimilates into the stem, root, rhizome, and NSCs. Activities of phosphoenolpyruvate carboxylase, ribulose-1, 5-diphosphate carboxylase, sucrose phosphate synthase (SPS) in flag leaf and adenosine diphosphate glucose pyrophosphorylase (AGPase) and SPS in the stem and rhizome all increased significantly. In contrast, activities of the AGPase in flag leaf and sheath decreased significantly. Contents of zeatin nucleoside, gibberellins, and indoleacetic acid in flag leaf, stem, and rhizome all increased. Abscisic acid contents in flag leaf and stem decreased significantly while increased significantly in the rhizome. In conclusion, growth-promoting hormones delayed plant senescence, enhanced leaf photosynthesis, and enhanced vegetative growth through regulating assimilates-metabolism-related enzymes, which increased biomass accumulation in PR switchgrass. This work provided new insights for yield and digestibility improvement in switchgrass through field management practices, hormones regulation, or genetic modification strategies.

Nitrogen enhances the effect of pre-drought priming against post-anthesis drought stress by regulating starch and protein formation in wheat.

Drought stress is one of the most serious environmental stress factor constraining crop production across the globe. Among cereals, wheat grains are very sensitive to drought as a small degree of stress can affect the enzymatic system. This study aimed to investigate whether nitrogen and pre-anthesis drought priming could enhance the action of major regulatory enzymes involved in starch accumulation and protein synthesis in bread wheat (Triticum aestivum L.). For this purpose, cultivars YM-158 (medium gluten) and YM-22 (low gluten) were grown in rain-controlled conditions under two nitrogen levels, that is, N180 (N1) and N300 (N2). Drought priming was applied at the jointing stage and drought stress was applied 7 days after anthesis. Drought stress reduced starch content but enhanced protein content in grains. N2 and primed plants kept higher contents of nonstructural carbohydrates, fructans, and sucrose; with higher activity of sucrose-phosphate synthase in flag leaves. Furthermore, N2 and priming treatments showed higher sink ability to develop grains by showing higher sucrose-to-starch conversion activities of adenosine diphosphate-glucose pyrophosphorylase, uridine diphosphate glucose pyrophosphorylase, sucrose-synthase, soluble-starch synthase, starch branching enzyme, and granule-bound starch synthase as compared to N1 and non-primed treatments. The application of N2 and primed treatment showed a greater ability to maintain grain filling in both cultivars as compared to N1 and non-primed crops. Our study suggested that high nitrogen has the potential to enhance the effect of pre-drought priming to change source-sink relationships and grain yield of wheat under drought stress during the filling process.

Fruit growth, carbon allocation, and related enzymes in tomato under different irrigation and potassium application regimes

AbstractBackgroundThe increasing concentration of atmospheric CO2 not only affects the growing environment of crops but also aggravates the global greenhouse effect and further aggravates the problem of water shortage. The combined effect of water deficit and potassium (K) application has not been widely studied.AimsA pot experiment was conducted to investigate the effect of deficit irrigation (DI) and K application at different growth stages on carbon allocation and enzyme activities related to sugar metabolism.MethodsTomatoes were transplanted and planted on April 26, 2017 and harvested on August 15, 2017. Four irrigation regimes were implemented with two water levels (full irrigation‐W and DI‐W/2) in different growth stages, and each water treatment was equally divided into two subgroups: with K (K1) and without K (K0). Fruits from the first to fourth trusses of the tomato plants were sampled. Tomato growth, carbon allocation, and related enzyme activities were measured.ResultsThe fresh weight (FW), dry weight, and relative growth rate of dry mass were sensitive to irrigation amount under K fertilization, enhancing the promotion effect of irrigation on fruit. Meanwhile, carbon allocation was sensitive to irrigation amount under K regime. Sucrose synthase (SuSy), acid invertase (AI), and sucrose phosphate synthase (SPS) were also highly sensitive to irrigation amount under K application condition. Starch phosphorylase displayed a quadratic parabola for irrigation amount, and adenosine diphosphate glucose pyrophosphorylase (AGPase) was highly sensitive to irrigation amount without K fertilization. Carbon in the form of other carbohydrates, carbon in the form of soluble sugar (Csol), and fruit water content were the factors that had the greatest influence on the principal components. Classification by K‐means algorithm and canonical correlation analysis showed that FW, fructose, sucrose, and starch could be used as significant indicators of the dry matter components of the fruit for the treatment without K. In the case of K regime, SuSy, AGPase, AI, and Csol could be used as a significant indicator of the correlation analysis of carbon metabolism activity.ConclusionsThe factors related to the improvement of fruit quality and carbon allocation by deficient irrigation and K application were explored. Water stress changed the distribution of photosynthetic carbon between starch and soluble sugar. K application further changed the balance between soluble sugars and other compounds. In particular, it significantly increased the carbon content of soluble sugars and decreased that of other compounds. AI and SuSy are key enzymes affecting carbon metabolism under water‐deficient conditions.

Agronomic and Physicochemical Properties Facilitating the Synchronization of Grain Yield and the Overall Palatability of Japonica Rice in East China

Understanding the agronomic and physicochemical characteristics related to grain yield and grain quality is an ongoing hotspot. In 2018 and 2019, high-yielding rice with good palatability (HYGP), high-yielding rice with poor palatability (HYPP), and low-yielding rice with good palatability (LYGP) were grown in paddy fields to explore the main traits underlying the better grain yield and overall palatability of HYGP. HYGP and HYPP demonstrated a 18.1–20.7% higher grain yield (p < 0.05) than LYGP; HYGP and LYGP gave an overall palatability from 75.2 to 77.0, higher (p < 0.05) than HYPP. The higher grain yield of HYGP compared to that of LYGP resulted from a larger sink size because of the spikelets per panicle and the higher total shoot biomass weight (p < 0.05). HYGP exhibited more (p < 0.05) panicles per m2 but lower spikelets per panicle and 1000-grain weight than HYPP and maintained a similar grain yield to HYPP. Compared with HYPP and LYGP, HYGP exhibited more (p < 0.05) biomass accumulation from heading to maturity, supported by the higher leaf area index, post-heading leaf photosynthetic rate, and SPAD values. HYGP had higher (p < 0.05) adenosine diphosphate glucose pyrophosphorylase and starch branching enzyme activities at the middle and late grain-filling stages than HYPP and LYGP. HYGP and LYGP had a lower (p < 0.05) chalky area, chalky degree, amylose content, setback, grain protein content, and prolamin content than HYPP, while it had a higher (p < 0.05) gel consistency, breakdown, and ratio of glutelin content to prolamin content. Our results suggested that optimized yield components, more biomass accumulation through improved leaf photosynthetic capacities, a lower amylose content with coordinated enzyme activities involved in starch synthesis, and a lower grain protein content with a better composition were the main traits facilitating the better grain yield and overall palatability of rice in east China.

Excessive nitrogen in field-grown rice suppresses grain filling of inferior spikelets by reducing the accumulation of cytokinin and auxin

Excessive nitrogen fertilizer is often applied to achieve higher rice yield in many regions of the world. However, the effect of excessive nitrogen on grain filling of inferior spikelets and its underlying mechanisms are still poorly understood. A three-year field experiment was conducted to reveal the mechanisms by which excessive nitrogen application regulated grain filling. We found that excessive application of nitrogen reduced the starch biosynthesis and grain weight of inferior spikelets but not superior spikelets. Plant hormone detection revealed that both cytokinin (CTK) and 3-Indoleacetic acid (IAA) were reduced by excessive nitrogen at the early stage of grain filling in inferior spiekelts. Quantitative real-time PCR results showed that inhibition of biosynthesis genes led to a decrease in IAA content, while elevation of CTK oxidase genes resulted in a lower level of CTK under excessive nitrogen treatment. Application of exogenous IAA or CTK significantly impaired the inhibitory effect of excessive nitrogen on starch accumulation and grain weight of inferior spikelets. Further enzyme assays revealed that excessive nitrogen application significantly suppressed the enzyme activities of sucrose synthase (SuS), adenosine diphosphate glucose pyrophosphorylase (AGP) and starch synthase (StS) in inferior spikelets. Application of exogenous IAA or CTK to the panicle under excessive nitrogen treatment significantly increased the enzyme activities of SuS, AGP and StS. Taken together, our results revealed that excessive nitrogen application in field-grown rice suppressed grain filling of inferior spikelets by reducing the accumulation of cytokinin and auxin. • Grain filling of inferior spikelets was reduced by excessive nitrogen application. • HN application reduced the contents of CTK and auxin in inferior spikelets at 6 DAA. • Exogenous CTK and auxin both increased grain filling under HN conditions. • HN downregulated auxin biosynthesis genes while upregulated CTK catabolism genes. • Activities of key enzymes for starch biosynthesis were regulated by CTK and auxin.

Activities of Key Enzymes Involved in Starch Accumulation In Sorghum (Sorghum Bicolor L. Moench) Grains With Different Starch Contents

Starch accumulation and the seven metabolic enzyme activities in sorghum grains with different starch contents were investigated under field conditions in Shenyang Agricultural University. The results indicated that the starch accumulation in Tieza17 (high starch content variety) and Liaoza11 (low starch content variety) grains could be fitted with logistic equation. The activities of sucrose synthase (SS), soluble starch synthase (SSS) and uridine diphosphate glucose pyrophosphorylase (UGPase) in Tieza17 were similar to those in Liaoza11. Adenosine diphosphate glucose pyrophosphorylase (AGPase) and granule-bound starch synthase (GBSS) activities in Tieza17 grains were consistently higher than those in Liaoza11 grains. Starch branching enzyme (SBE) and starch debranching enzyme (DBE) activities increased or decreased significantly between the two varieties at different filling stages. It is suggested that the differences in the activities of AGPase, GBSS, SBE and DBE and their tradeoff played an important role in regulating starch accumulation in sorghum grains. Bangladesh J. Bot. 51(2): 217-222, 2022 (June)

Post‐anthesis saline‐alkali stress inhibits grain filling by promoting ethylene production and signal transduction

AbstractSaline‐alkali stress is one of the major abiotic stresses that severely affect rice yield. However, the mechanism by which saline‐alkali stress regulates grain filling in rice is still unclear. In this study, Oryza sativa L. spp. Indica cultivar Chaoyou1000 (C1000) was exposed to post‐anthesis saline‐alkali conditions at 6 days after anthesis, which significantly reduced the grain weight by suppressing the accumulation of starch and non‐structural carbohydrates in grains. Further analysis found that 1‐aminocyclopropane‐1‐carboxylate (ACC), a precursor for ethylene, was increased by saline‐alkali treatment. qRT‐PCR results showed that several key genes involved in ethylene biosynthesis, including the OsACS and OsACO genes, were upregulated in saline‐alkali‐treated grains. In addition, genes involved in the ethylene signalling pathway were also induced by saline‐alkali stress. Exogenous ethylene application reduced grain weight and both starch and NSC contents in grains of C1000, suggesting that saline‐alkali‐induced ethylene has a negative effect on grain filling. Furthermore, the gene expression levels of OsSUS, OsAGPL, OsAGPS, OsSSI and OsSSIIIa, which are key genes in the starch biosynthesis pathway, were downregulated in saline‐alkali‐treated grains. In agreement, assays on these enzymes further revealed that saline‐alkali stress decreased the activities of sucrose synthase (SUS), adenosine diphosphate glucose pyrophosphorylase (AGP) and starch synthase (StS). Together, our results indicated that saline‐alkali stress suppressed the enzyme activities involved in the conversion of sucrose to starch by elevating ethylene production, which led to inhibition of grain filling.

Stem small vascular bundles have greater accumulation and translocation of non-structural carbohydrates than large vascular bundles in rice.

Phloem unloading and loading are associated with stem non-structural carbohydrates (NSCs) accumulation and remobilization in rice (Oryza sativa L.). Four rice recombinant inbred lines (R032, R191, R046, and R146) derived from a cross between Zhenshan 97 and Minghui 63 were used to investigate the contributions of stem large and small vascular bundles (SVBs) to NSCs accumulation and translocation. Before heading, the parenchyma cells in stem cortex tissues (PCs) surrounding SVBs had higher starch density than those surrounding large vascular bundles (LVBs). Moreover, the protein levels of sucrose transporters (SUTs), cell wall invertase, sucrose synthase, and adenosine diphosphate glucose pyrophosphorylase, as well as the phloem plasmodesma densities were higher in SVBs than those in LVBs. After heading, starch density decreased more in PCs surrounding SVBs than in LVBs. Also, the protein levels of SUTs, α-amylase, sucrose phosphate synthase and sucrose synthase, the phloem plasmodesma densities in SVBs were higher than those in LVBs. The correlations of the number and total cross-sectional area of SVBs with mass and contribution to yield of transferred NSCs were higher than those of LVBs. Our results suggest that SVBs may have higher contributions to pre-anthesis stem NSCs accumulation and post-anthesis translocation than LVBs, which is potentially attributed to the high level of protein and enzyme involved in stem unloading and loading via apoplastic and symplastic pathways.

Changes of starch and sucrose content and related gene expression during the growth and development of Lanzhou lily bulb.

As the main forms of carbohydrates, starch and sucrose play a vital role in the balance and coordination of various carbohydrates. Lanzhou lily is the most popular edible lily in China, mainly distributed in the central region of Gansu. To clarify the relationship between carbohydrate metabolism and bulb development of Lanzhou lily, so as to provide a basis for the promotion of the growth and development in Lanzhou lily and its important economic value, we studied lily bulbs in the squaring stage, flowering stage, half withering stage and withering stage. The plant height, fresh weight of mother and daughter bulbs continued to increase during the whole growth period and fresh weight of stem and leaf began to decrease in the half withering stage. The content of starch, sucrose and total soluble sugar in the lily mother bulb accumulated mostly in the flowering, withering and half withering stages, respectively. Starch, sucrose and total soluble sugar accumulated in the daughter bulb with the highest concentration during the withering stage. In the transcription level, sucrose synthase (SuSy1) and sucrose invertase (INV2) expressed the highest in squaring stage, and the expression was significantly higher in the mother bulb than in the daughter bulb. In flowering stage, the expression levels of soluble starch synthase (SSS1), starch-branching enzyme (SBE) and adenosine diphosphate-glucose pyrophosphorylase (AGP1) genes were higher in the mother bulb than in the daughter bulb. Altogether, our results indicate that starch and sucrose are important for the bulb growth and development of Lanzhou lily.

The Effects of Short-Term Exposure to Low Temperatures During the Booting Stage on Starch Synthesis and Yields in Wheat Grain.

Low temperatures (LT) in spring can have a major impact on the yields of wheat in winter. Wheat varieties with different cold sensitivities (the cold-tolerant Yannong 19 variety and the cold-sensitive Yangmai 18 variety) were used to study the responses of the wheat grain starch synthesis and dry material accumulation to short-term LT during the booting stage. The effects of short-term LT on the activities of key wheat grain starch synthesis enzymes, starch content and grain dry-matter accumulation were determined by exposing the wheat to simulated LT of from −2 to 2°C. Short-term LT stress caused a decrease in the fullness of the wheat grains along with decreased activities of adenosine diphosphate glucose pyrophosphorylase (AGPase, EC2.7.7.27), soluble starch synthase (SSS, EC2.4.1.21), granule-bound starch synthase (GBSS, EC2.4.1.21), and starch branching enzyme (SBE, EC2.4.1.18) at different spike positions during the filling stage. The rate of grain starch accumulation and starch content decreased with decreasing temperatures. Also, the duration of grain filling increased, the mean and the maximum filling rates were reduced and the quality of the grain dry-matter decreased. The number of grains per spike and the thousand-grain weight of the mature grains also decreased. Our data showed that short-term LT stress at the booting stage caused a decrease in the activities of key starch synthesis enzymes at the grain-filling stage. These changes reduced the accumulation of starch, decreased the filling rate, and lowered the accumulation of grain dry matter to ultimately decrease grain yields.

The Associated With Carbon Conversion Rate and Source-Sink Enzyme Activity in Tomato Fruit Subjected to Water Stress and Potassium Application.

Carbon metabolism in higher plants is a basic physiological metabolism, and carbon allocation and conversion require the activity of various enzymes in metabolic processes that alter the content and overall composition of sugars in the sink organ. However, it is not known how various enzymes affect carbon metabolism when tomato plants are subjected to water stress or treated with potassium. Although the process of carbon metabolism is very complex, we used the carbon conversion rate to compare and analyze the enzyme activities related to sugar metabolism and find out which carbon conversion rate are the most important. Results showed that water stress and potassium increased carbon import flux in the fruit, which was beneficial to carbon accumulation. Water deficit increased the activity of sucrose synthase (SuSy) and starch phosphorylase (SP) and decreased the activity of sucrose phosphate synthase (SPS) and adenosine diphosphate glucose pyrophosphorylase (AGPase) in the source. Water stress increased the activity of acid invertase (AI), SuSy and SP but decreased the activity of AGPase in the sink. Potassium modified the balance of enzymes active in sugar and starch metabolism by increasing the activity of AI, SuSy, SPS and SP and significantly decreasing the activity of AGPase, resulting in increase of hexose. Canonical correlational analysis revealed that the carbon conversion rate was mainly affected by the relative rate of conversion of sucrose to fructose and glucose [p1(t)] and glucose to starch [p5m(t)]. SuSy and AGPase had the greatest effect on enzyme activity in the fruit; respectively regulated p1(t) and p5m(t).

Increase in carbohydrate content and variation in microbiome are related to the drought tolerance of Codonopsis pilosula

Drought stress is one of the main limiting factors in geographical distribution and production of Codonopsis pilosula. Understanding the biochemical and genetic information of the response of C. pilosula to drought stress is urgently needed for breeding tolerant varieties. Here, carbohydrates, namely trehalose, raffinose, maltotetraose, sucrose, and melezitose, significantly accumulated in C. pilosula roots under drought stress and thus served as biomarkers for drought stress response. Compared with those in the control group, the expression levels of key genes such as adenosine diphosphate glucose pyrophosphorylase, starch branching enzyme, granule-bound starch synthase, soluble starch synthase, galacturonate transferase, cellulose synthase A catalytic subunit, cellulase Korrigan in the carbohydrate biosynthesis pathway were markedly up-regulated in C. pilosula roots in the drought treatment group, some of them even exceeded 70%. Notably, and that of key genes including trehalose-6-phosphatase, trehalose-6-phosphate phosphatase, galactinol synthase, and raffinose synthase in the trehalose and raffinose biosynthesis pathways was improved by 12.6%–462.2% in C. pilosula roots treated by drought stress. The accumulation of carbohydrates in C. pilosula root or rhizosphere soil was correlated with microbiome variations. Analysis of exogenous trehalose and raffinose confirmed that increased carbohydrate content improved the drought tolerance of C. pilosula in a dose-dependent manner. This study provided solid foundation for breeding drought-tolerant C. pilosula varieties and developing drought-resistant microbial fertilizers.

Proteomic analysis reveals a role of ADP-glucose pyrophosphorylase in the asynchronous filling of rice superior and inferior spikelets

The poor grain filling of inferior spikelets (IS) situated on the lower secondary rachis branch leads to a remarkable decrease in rice yield and quality. The AGPase small subunit 2 (AGPS2) encodes a small subunit of adenosine diphosphate-glucose pyrophosphorylase (AGPase) enzyme, which plays an important role in sucrose-starch conversion and starch biosynthesis in the grain filling of rice. In the present study, qPCR analysis showed low expression abundance of AGPS2 in IS, compared to the superior spikelets (SS), which was consistent with the lower grain weight of IS. To evaluate the molecular mechanism of AGPS2, we first identified the AGPS2 interaction network through Co-immunoprecipitation (Co-IP). In total, 29 proteins of AGPS2 interaction network were characterized by LC–MS/MS. Bioinformatics analysis revealed that, the characterized proteins in the interaction network are likely to be related to starch synthesis, sugar conversion, energy pathway, and folding/modification, and most of them were involved in the grain filling of rice. The sequent Co-IP analysis showed that AGPS2 can bind to starch branching enzyme (SBE), pullulanase (PUL) and starch debranching enzyme (DBE) and assemble into starch synthesizing protein complex (SSPC). In addition, the 14-3-3 protein GF14e was also found to interact with AGPS2. Further analysis by qPCR showed that the expression of GF14e was much higher on IS than on SS. The qPCR results also showed that the expression of GF14e was relatively stable in SS, but changed significantly in IS under alternate wetting and moderate soil drying (WMD), which is consistent with the AGPS2 expression pattern. Our present work provides direct molecular evidence for the different expression patterns of AGPS2 in SS and IS, which could be greatly helpful for the molecular amelioration of the poor grain filling of IS in rice.

Removal of superior wheat kernels promotes filling of inferior kernels by changing carbohydrate metabolism and sink strength

Poor filling and low weight of inferior kernels limit the further improvement of wheat yield. Two cultivars, Shuangda 1 and Xinong 538, with different grain weights, were selected to investigate the physiological changes of inferior kernels by removal of superior kernels (RS) at the flowering stage. iTRAQ combined with physiological indexes was used to identify factors limiting the filling of inferior kernels. Removal of superior kernels significantly increased the mean filling rate of inferior kernels and thus increased their weight. A set of 6012 proteins in inferior wheat kernels were differentially expressed between the RS and control. These differentially expressed proteins were involved mainly in carbon metabolism and energy metabolism. The main reason for the promoting effect of RS on the filling of inferior kernels may be that RS downregulated proteins involved in glycolysis and pyruvate metabolism while upregulating proteins involved in carbon fixation and photosynthesis. Consequently, RS greatly increased the ATP content in inferior kernels, supplying energy for them to absorb photosynthetic assimilates. Removal of superior kernels increased the activities of sucrose synthase, soluble starch synthase, adenosine diphosphate glucose pyrophosphorylase, and starch branching enzyme in inferior kernels and promoted starch accumulation in them. Thus, RS promoted the filling of inferior kernels and increased their weight. The promoting effect of RS on starch synthesis in inferior kernels was associated with their endogenous IAA and ABA levels.

Effects of Fe-Mn oxide-modified biochar composite applications on phthalate esters (PAEs) accumulation in wheat grains and grain quality under PAEs-polluted brown soil

Phthalate esters (PAEs), such as dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), are used extensively as additives and plasticizers, and have become ubiquitous in the environment. PAEs in the soil could have adverse effects on crop plants as well as humans via accumulations in food chain. Thus, it is important to explore strategies to reduce the bioavailability of phthalate esters. We investigated the effects of Fe-Mn oxide-modified biochar composite (FMBC) applications on the quality of wheat grown in DBP- and DEHP-polluted brown soil. The application of FMBC and biochar (BC) increased the wheat grain biomass by 9.71–223.01% and 5.40–120.15% in the DBP-polluted soil, and 10.52–186.21% and 4.50–99.53% in the DEHP-spiked soil in comparison to the controls. All FMBC treatments were better than the BC treatments, in terms of decreasing DBP and DEHP bioavailability for the wheat grains. The activities of the glutamine synthetase and glutamic-pyruvic transaminase in the flag leaves at the filling stage and of granule-bound starch synthase, soluble starch synthase, and adenosine diphosphate-glucose pyrophosphorylase in the grains at maturity increased significantly with increases in either the BC or FMBC applications. This, in turn, increased the starch, protein, and amino acid content in the wheat grains. Compared with the BC treatment, the FMBC amendment induced only slight increases in the aforementioned factors. This study offers novel insights into potential strategies for decreasing PAEs bioavailability in soil, with potential positive implications for crop quality and environmental health improvements.